Traumatic brain injury is the most common cause of death in childhood, yet etiology and treatment of pediatric head injuries remain controversial. Previously, we established an interdisciplinary research paradigm using acute animal experiments, biomechanical tissue tests, retrospective clinical studies, anthropomorphic "doll" studies, and computational simulations. Our data show that children do indeed have injury mechanisms that are distinct from the adult, and require age-specific injury prevention strategies and treatments. In this competitive renewal, we build on the foundation we have established, both to deepen our understanding of basic injury mechanisms and to enhance the clinical relevance of our findings. We will supplement our current platforms with novel preparations - survival studies, porcine behavioral outcomes, cerebral blood flow (CBF) measures, post-injury respiratory insufficiency, and injury treatment studies - to enhance translation of research findings from the laboratory to the clinical setting. Our overall hypothesis is that rapid rotations of the immature brain without impact produce brain injury via both mechanical and biochemical signals, resulting in sustained functional and histological abnormalities. We will compare long-term outcomes after single and multiple head injuries to determine if injury interval modulates injury severity and if axonal injury is reduced with folate supplementation (Aim 1). We will use human computational models to extend our animal studies to cyclic shaking motions to estimate contribution of harmonic amplification to injury risk (Aim 2). Using animal experiments and computer models, we will identify cerebral strains associated with rapid regional decreases in CBF and brainstem deformations associated with loss of cerebral autoregulation (Aim 3). We will modulate regional deformations by altering rotation direction, and endothelial response with hypertonic saline to validate acute mechanical and biochemical signaling pathways. In piglets with respiratory insufficiency after head injury (Aim 4), we hypothesize that resuscitation with 100% FiO2 results in exacerbated neuropathology mediated by free radical release, and we will compare outcomes with room air and 100% FiO2, as well as with and without free radical scavengers to verify functionality. The proposed studies address our long-term goal of elucidating injury mechanisms and potential treatment strategies for traumatic brain injuries in children.